Millimeter wave radar devices find increasing use in e.g., automobile applications. A radar system may generally comprise a transmitter for emitting a radar signal and a detector for receiving and analyzing a reflected part of the radar signal. The expression “radar device” as used herein, may refer to a transmitter section or a detector section or a combination of both of a radar system. A radar system may comprise multiple antennas for improving the accuracy of a map of objects produced by the radar system. The antennas may, for example, be operated sequentially.
An example of a radar transmitter device 10 is shown in FIG. 1. The radar device 10 may comprise a radar frequency (RF) signal source 12, a feed network 13, two or more power amplifiers 14, 16, and a corresponding set of antennas 22, 24. The signal source 12 may, for example, comprise an oscillator core, e.g., a VCO (voltage-controlled oscillator). The RF signal may have a frequency higher than e.g., ten gigahertz or even higher than, e.g., seventy six gigahertz. The radar device 10 may further comprise a control unit 15 for activating and deactivating selected ones of the power amplifiers 14, 16. A control unit 15 may, for example, receive or generate a selection signal (SEL) for specifying either a first transmission channel associated with, e.g., the first transmission antenna 22 or a second transmission channel associated with, e.g., the second transmission antenna 24. For example, when the first antenna 22 has been selected for transmission, the control unit 15 may switch the first power amplifier 14 on and the second power amplifier 16 off. As a consequence, the first transmission antenna 22 may be provided with an amplified radar frequency signal by the first power amplifier 14, while the second transmission antenna 24 will be provided with no signal from the second power amplifier 16 in an ideal scenario.
In practice, however, there may be so-called crosstalk or a leakage signal, due to limited isolation of the power amplifier in the microwave and millimeter-wave frequency range and electromagnetic (EM) coupling of passive elements between the antennas 22, 24. That is, a portion of the radar frequency (RF) signal may travel to the second antenna 24 via, e.g., the feed network 13 and also a portion of the amplified radar frequency output signal by the first power amplifier 14 may travel to the second antenna 24 via, e.g. coupling, and be transmitted by the second antenna 24, although in this example only the first antenna 22 is selected as the active one. The power level difference or power suppression between two antenna ports when one antenna is on and another one is off can be an essential parameter for the system performance.
Turning now to FIG. 2, an example of a radar receiver device 10 is shown. The basic structure of the receiver device may be similar to the transmitter device 10 described above in reference to FIG. 1. The present radar device 10 may comprise a signal source 12, e.g., a local oscillator (LO) connected to two or more mixers 14, 16 via a feed network 13. The mixers 14, 16 may each be connected to a corresponding reception antenna 22, 24. Each mixer, e.g., mixer 14 may be arranged to mix the radar frequency signal from the signal source 12 with a reception signal received from the corresponding antenna, e.g., the first antenna 22, to generate an intermediate frequency (IF) signal which may then be further processed and analyzed. Each of the mixers 14, 16 may comprise an amplifier (not shown), e.g., a low noise amplifier, for amplifying the reception signal received by the corresponding antenna. A control unit 15 may be provided to activate or deactivate a selected one of the mixers 14, 16, thereby selecting one of the antennas 22, 24 as an active antenna. However, crosstalk between the two branches 14, 22, and 16, 24 may deteriorate the quality of the intermediate frequency signal generated by the active branch.